The present invention relates to a polishing cloth used in a chemical mechanical polishing (CMP).
Recently, a CMP method for flattening a surface of an insulating layer or a wiring layer has attracted attention in this technical field.
A known polishing cloth used in the CMP method includes xe2x80x9cPolitex,xe2x80x9d (trade name of a polishing cloth manufactured by Rodel Inc.) which does not require a pad conditioning treatment (dressing). Politex has a cross sectional shape resembling an arrangement of octopus traps and, thus, is excellent in its capability of retaining a slurry used for polishing, where said slurry contains water, SiO2, Al2O3, and chemicals (oxidizing agent), etc. Also, Politex has a very flexible surface and, thus, does not impart sharp scratches to the surface of the polished material.
However, Politex has a very low compression modulus of elasticity, which is less than 10 MPa, and, thus, is very soft. Therefore, when Politex is used in a flattening process of a target object to be flattened, the polishing rate is very low and the flatness of the target object after the polishing treatment is not satisfactory.
The known polishing cloths also include xe2x80x9cIC-1000xe2x80x9d (trade name of a polishing cloth manufactured by Rodel Inc.). Voids are formed within IC-1000. Also IC-1000 has a compression modulus of elasticity of about 200 MPa and, thus, is considerably harder than Politex.
In general, a pad conditioning treatment using a diamond conditioning plate is applied to the polishing cloth IC-1000 for polishing a semiconductor wafer. In the pad conditioning treatment, the surface layer of the polishing cloth IC-1000 is scratched to form a soft surface layer. If the pad conditioning treatment is not applied to IC-1000, IC-1000 has a hard surface layer, leading to a low capability of retaining a slurry and, thus, to a markedly low polishing rate. Naturally, the life of the polishing cloth IC-1000 is determined by the number of pad conditioning treatments applied thereto because the surface layer of the polishing cloth IC-1000 is scratched every time the pad conditioning treatment is applied to the polishing cloth IC-1000.
Where the polishing cloth IC-1000 subjected to a pad conditioning treatment that is used for polishing 1000 wafers, the surface layer of IC-1 000 is lost in a thickness of about 850 xcexcm. Where the pad conditioning treatment is applied to the polishing cloth IC-1000 under milder conditions for ensuring a longer life of IC-1000, the polishing rate is lowered or rendered unstable.
It should be noted that a soft layer having a compression modulus of elasticity of 10 MPa or less is formed in a thickness of scores of microns in the surface region of the polishing cloth IC-1000 immediately after the pad conditioning treatment. The particular soft layer impairs the flatness on the polished surface of the target object.
Further, the soft layer is compressed during the polishing treatment so as to be hardened with the progress of the polishing treatment. Since the surface region is hardened, the scratches generated on the surface region of the polishing cloth IC-1000 are enlarged with progress of the polishing treatment, though the scratch occurrence on the soft surface region is suppressed immediately after initiation of the polishing treatment.
As described above, a soft surface layer is formed in the polishing cloth represented by Politex, with the result that the polishing rate is low and the polished target object is not satisfactory in the surface flatness, though scratches are not formed on the target object.
On the other hand, the polishing cloth represented by IC-1000 is defective in that, if a pad conditioning treatment is not applied to the polishing cloth, many scratches are formed on the target object with progress of the polishing treatment. If a pad conditioning treatment is applied to the polishing cloth, however, the surface region of the polishing cloth is scratched off. Naturally, the polishing cloth is thinned, leading to a short life of the polishing cloth.
Further, if a semiconductor wafer is polished by using the conventional polishing cloth for forming, for example, a buried wiring (damascene wiring), dishing or thinning is brought about by an over-polishing so as to generate the so-called xe2x80x9cdishingxe2x80x9d. The dishing causes a short-circuiting of the wiring formed in an upper layer in the lithography process. Also, the wiring formed on the dished or thinned surface is rendered longer, leading to an increased resistance of the wiring.
An object of the present invention is to provide a polishing cloth that permits flattening the surface of a target object at a high accuracy, permits achieving a stable polishing rate, and permits suppressing the scratch occurrence in the target object, and a method of manufacturing a semiconductor device using the particular polishing cloth.
According to an aspect of the present invention, which is intended to achieve the above-noted object, a polishing cloth is provided comprising a base body holding a slurry on the surface and serving to mechanically polish a surface of a target object to be polished, and fine particles dispersed in the base body and soluble in a solvent.
According to another aspect of the present invention, a polishing cloth is provided, comprising fine particles soluble in a solvent, and a base body having the fine particles dispersed therein and holding a slurry on the surface, the fine particles being dissolved in the solvent when a surface of a target object is mechanically polished by the polishing cloth so as to form concavities on the surface of the polishing cloth.
According to another aspect of the present invention, a method of manufacturing a semiconductor device is provided by using a polishing cloth, comprising the steps of forming an insulating film on a substrate, followed by forming a wiring groove on the substrate through the insulating film, forming a metal wiring layer on the substrate and in the wiring groove, burying the metal wiring in the wiring groove, and mechanically polishing the metal wiring buried in the wiring groove with a polishing cloth so as to remove an undesired portion of the metal wiring and, thus, to flatten the surface of the metal wiring, the polishing cloth comprising a base body holding a slurry on the surface and serving to mechanically polish a surface of a target object to be polished, and fine particles dispersed in the base body and soluble in a solvent.
Further, according to still another aspect of the present invention, a method of manufacturing a semiconductor device is provided by using a polishing cloth, comprising the steps of forming a groove in a substrate, forming an insulating film on the substrate such that the insulating film is buried in the groove, and polishing the insulating film by using a polishing cloth so as to remove an undesired portion of the insulating film, thus, to flatten the surface of the insulating film, the polishing cloth comprising a base body holding a slurry on the surface and serving to mechanically polish a surface of a target object to be polished, and fine particles dispersed in the base body and soluble in a solvent.
In the polishing cloth of the present invention, fine particles soluble in a solvent are dispersed in a base body serving to mechanically polish a target object. During the polishing operation, the fine particles exposed to the surface of the base body are dissolved in a solvent such as water to form concavities holding a slurry on the surface of the base body. It follows that the polishing cloth of the present invention permits flattening the surface of the target object highly accurately at a high polishing rate. In addition, the scratch formation can be suppressed on the surface of the polished target object.
In the method of the present invention for manufacturing a semiconductor device by using the particular polishing cloth, a wiring groove is formed in a substrate, followed by burying a metal wiring in the wiring groove. Then, the undesired portion of the metal wiring is removed by polishing with the polishing cloth having fine particles soluble in a solvent dispersed in a base body, thereby improving the quality of the wiring, particularly, a damascene wiring.
Further, the method of the present invention for manufacturing a semiconductor device by using the particular polishing cloth can also be applied to the case where an oxide film is buried in place of the metal wiring in the wiring groove. In this case, the oxide film is polished by the polishing cloth to flatten the surface of the oxide film satisfactorily.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.